Abstract
In this work, broadband optical frequency comb (OFC) generation by a gain-switching vertical-cavity surface-emitting laser (VCSEL) subject to optical injection is investigated experimentally. During implementing the experiment, a 1550 nm VCSEL under a large signal current modulation is driven into the gain-switching state with a broad noisy spectrum. By further introducing an optical injection, a high performance OFC can be produced. The experimental results demonstrate that the power and wavelength of the injection light seriously affect the performance of the produced OFC. Under proper optical injection parameters, two sub-combs originating from two orthogonal polarization components of the VCSEL can splice into a broadband total-OFC. By selecting optimized operation parameters, a high quality total-OFC can be acquired, with stable comb lines, high coherence, wide bandwidth of 70.0 GHz (56.0 GHz) within 10 dB (3 dB) amplitude variation and low single sideband phase noise at the fundamental frequency below −120.6 dBc/Hz @ 10 kHz.
Highlights
Optical frequency comb (OFC) is composed of a series of spaced discrete comb lines, and these discrete comb lines corresponding to different frequency components can be simultaneously provided in a frequency band [1]
optical frequency comb (OFC) with good stability, high degree of coherence, as well as high repetition rates have been extensively applied in spectroscopy, metrology, optical communication, THz generation, optical arbitrary waveform generation, and other fields [1,2,3,4,5,6,7,8,9,10,11,12,13,14]
To further extend the optical span of the total-OFC, the research group proposed that an optical injection is introduced into the gain-switching vertical-cavity surface-emitting laser (VCSEL), and the results showed that an OFC with enhanced optical span can be obtained by carefully adjusting the polarization of optical injection [34,35]
Summary
Optical frequency comb (OFC) is composed of a series of spaced discrete comb lines, and these discrete comb lines corresponding to different frequency components can be simultaneously provided in a frequency band [1]. Many approaches for generating OFCs have been proposed and investigated, such as mode-locking, external modulation, and gain-switching of semiconductor lasers [15,16,17,18,19,20,21,22,23]. By using external modulation of continuous wave light, an OFC with adjustable comb line spacing can be obtained. The approach for generating OFCs based on gain-switching semiconductor lasers has attracted much attention owe to the following advantages. On one hand, such an approach is easy to implement due to relatively simple experimental facility. The comb line spacing of the generated OFC is adjusted by varying the modulation frequency [26,27,28,29]
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